Bore sighting apparatus for large caliber guns



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J. B. NoLAN March 12, 1935.

BORE SIGHTING APPARATUS FOR LARGE CALIBER GUNS Filed April' 28, 1952 33. GEQMETHXCAL lNS TRUMEI lu.

Patented Mar. 12, 1935 UNITED STATES BORE SIGI-ITING APPARATUS FOR LARGE CALIBER GUNS James B. Nolan, United States Navy Application April 28, 1932, Serial No. 608,020

7 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) This invention relates to bore sighting apparatus and more particularly to a frame adapted to be mounted at the muzzle of a gun to support two collimators by which the gun sight telescopes may be adjusted until their axes are parallel to the bore of the gun.

An object of this invention is to provide bore sighting apparatus that does not require the use of a distant object on which to bore sight.

A second object is to provide bore sighting apparatus that can be used at sea as well as in smooth water and is not alTected by adverse conditions of visibility.

A third object is to provide bore sighting apparatus that renders the bore sighting more simple and the results more accurate.

With the above and other objects in view, this invention consists of such construction and arrangement of parts as will be more fully described in connection with the accompanying drawing, in which:

Fig. 1 is a plan View of a gun with telescopic sights showing the frame and collimators mounted at the muzzle;

Fig. 2 is a view in elevation of the apparatus shown in Fig. 1

Fig. 3 shows the arrangement for mounting the collimator frame in the muzzle of a gun;

Fig. 4 is a cross section of Fig. 3 at 4-fl;

Fig. 5 shows the effect of droop in the gun;

Fig. 6 is a side elevation of the collimator frame shown in Fig. 1;

Fig. 7 shows how the cross lines in the collimators can be graduated to bore sight at various ranges;

Fig. 8 is a perspective View of the expansible plug;

Fig. 9 is a cross section of Fig. 3 at 9-9.

In bore sighting guns on board ship, the customary method is to anchor the ship in still water at a distance from some prominent, easily visible object that is equal to the distance at which it is desired to bore sight, which is usually the mean range expected to be used in the next firing. A disk with a peep hole in its center is placed in the muzzle of the gun and appropriate supporting mechanism mounted at the breech for holding a bore sighting telescope so that its axis coincides with that of the gun. After the bore sighting telescope is mounted in the breech of the gun, it is adjusted by small set screws until its cross lines appear to be at the center of the peep hole. Since a large gun has a certain amount of droop, due to its length and weight, the line of the axis of the telescope will form a chord from the center of the breech to the center of the muzzle. The disk is then removed from the muzzle and the gun trained until the vertical line of the bore sight telescope is in line with one side of the prominent object and then both sight telescopes are adjusted until their vertical wires are also in line with that side of the object. The gun is then elevated until the horizontal line of the bore sighting telescope is in line with the top of the prominent object and the horizontal cross wires of the sight telescopes adjusted accordingly. It is evident that if there is any motion to the ship, this operation must be carried out by having a person stationed at each telescope, the one at the bore sight telescope to call out mark when his proper cross line is on the reference point, the other persons to note the amount the corresponding lines of their telescopes are off and to adjust their telescopes accordingly. After repeating such operations several times, the nal adjustment is arrived at. During this operation the sword arm or range scale has been maintained at its zero setting and the scale or deection scale at an arbitrary setting of 50, which is equivalent to zero setting of deliection, i. e. at this setting there is neither elevation or depression nor right or left deflection of the sight telescopes relative to the axis of the gun. The small set screws for adjusting the telescopes are not shown and form no part of this invention.

When these adjustments have been made for long ranges, the axis of the sight telescopes will be found to be practically parallel with the line from the center of the breech to the center of the muzzle. Such adjustments are called, bore sighting at infinity. It is known, however, for ranges under 2000 yards, there will be a noticeable convergence of the axis of the sight telescopes to the bore of the gun. Thus, in firing at long range, the gun is bore sighted at infinity, but in firing at short ranges it must be bore sighted for the mean range at which it is desired to re. In any case it is evident that the gun must be accurately bore sighted in order to make hits. The desirability of some method of bore sighting at sea and in poor visibility is readily seen, as well as a system to simplify and to reduce the time necessary for such operations. Such is the purpose of this invention.

Referring now to Fig. 1, 10 is the trainers telescope and 1l is the pointers telescope. The man stationed at 10 moves the gun in train about a vertical axis and the man stationed at llelevates and depresses the gun about a horizontal axis. The collimator frame l2 is mounted at the muzzle of the gun by the mechanism shown in Fig. 3.

Search ities It supports the collimators 13 and 14 so that their axes are parallel to the bore of the gun at the muzzle and at the same distance above and the same horizontal distance from the axis of the bore as the sight telescopes, as shown in Figs. 1 and 2. It is clear that when the gun sight telescopes are set for zero range and scale 50, and their axes are lined up with the corresponding axes of the collimator, the gun will be bore sighted for infinity.

'I'he mechanism for securing the collimator frame consists of an expansible plug 15, tapered hub 16, which is an integral part of frame 12 and securing bolt 17 with its nut 18. The expansible plug 15, Figs. 3 and 5, has six slots 26 extending almost the entire length of the plug, three starting from one end and the remaining three from the other end. The tapered hub 16 is advanced into plug 15 by turning nut 18 on bolt 17. This presses plug 15 tightly against the bore of the gun insuring the true alignment of the collimator frame 12. Plug 15 normally has a very snug t into the muzzle of the gun, so that very little expansion is necessary to make it tight. The key 19 prevents the turning of bolt 17 as nut 18 is tightened. The shoulder 20 makes the mounting more rigid and insures a more perfect alignment of the collimator frame.

When the collimator frame has been adjusted in position, the axes of the collimators will be parallel to the bore of the gun at the muzzle. This is the direction the projectile travels as it leaves the muzzle of the gun but it differs slightly from the chord from the center of the breech to the center of the muzzle as shown exaggerated in Fig. 5. This is one of the improvements of this apparatus, that the sight telescopes are lined up at zero range, scale 50 With the actual direction in which the projectile travels from the muzzle instead of the chord mentioned above that differs from this direction due to the droop of the gun. In Fig. 5, 21 is the chord 22, the actual direction in Which the projectile leaves the muzzle of the gun, and 23 the line of the telescope sights adjusted parallel to line 22.

In case it is desired to bore sight at ranges under 2000 yards, the collimators are graduated along their horizontal cross lines as shown in Fig. 7 to give the proper convergence of the sight telescopes to the axis of the bore of the gun. The graduations are marked with the ranges to which they correspond and in bore sighting for a particular range the cross lines of the sight telescope Would be adjusted to that mark on their respective collimators. In Fig. 7 the marks 24 are the marks giving the proper convergence for a range of 1800 yards.

When adjusting the collimator frame, use is made of lines 25 inscribed on the muzzle of the gun and pointers 28 inscribed on the collimator frame to see that the angular adjustment of the frame is proper. The collimators are further checked by bench marks 27, Fig. 2, on the sight telescope yoke directly over the axes of the sight telescopes. These marks are so located that With a scale of 50, when the sights are set at a predetermined range, the resulting depression of the sight yoke Will bring the bench marks 27 to the point through which the axes of the corresponding sight telescopes passed when the range was set at zero. It is now evident that if the cross lines of the collimators check on the bench marks, the axes of the collimators are parallel to the axis of the bore of the gun at the muzzle, and at positions through which the axes of the corresponding sight telescopes should pass when set to zero range and scale 50, since the accurate construction of the collimator frame is such that when properly oriented their axes are at the same distance above and the same horizontal distance from the axis of the bore of the gun as the axe of the corresponding sight telescopes.

After checking'the mounting of the collimators, the sight telescope yoke is again brought back to zero range and scale 50 and While in this position, by manipulation of the sight telescope screws (not shown), the cross wires of the sight telescopes are brought into alignment with the cross lines of the corresponding collimators or the proper range mark thereon. The sight telescopes are vthen secured in this position and the collimator frame and plug are removed, thus completing'thebore sighting of the gun.

The optical system of each collimator consists of an objective lens, a cross-line lens and an eyepiece system. The cross-line lens is placed in the focal plane of the objective lens to give a parallel beam of light which carries the image of the collimator cross lines and has the eect of producing a target or reference point at an innite distance from the gun sight telescope. This effect permits the gun sight telescopes to be focused on a reference point, dened by the intersection of the collimator cross lines, actually established at the muzzle of the gun but apparently at infinity. When the device is removed, the gun sight telescope Will be in correct focus Without further adjustment for a target at an innite distance beyond the anterior focus of the gun sight telescope. It is understood that the term collimator as used throughout the specification and claims embraces the optical system as just described.

While in the foregoing there has been illustrated and described such combination and arrangement of elements as constitute the preferred ernlbodiment of my invention, it is nevertheless desired to emphasize the fact that interpretation of the invention should be conclusive only when made in the light of the subjoined claims.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes Without the payment to me of any royalties thereon.

I claim:

1. Bore sighting apparatus, comprising a plug adapted to t within the muzzle of a gun, a co1- limator supporting arm having a tapered hub adapted to t into said plug, reference means on the muzzle end of the gun for approximately positioning said collimator supporting arm, a collimator at each end of said supporting arm, reference means on the breech end of the gun for accurately aligning said collimator, means for xedly securing said plug and collimator supporting arm in the gun muzzle, said means comprising a bolt and nut for drawing the tapered hub into said plug to expand the same Within the muzzle, and cooperating means in said supporting arm and said bolt for preventing relative rotation therebetween.

2. A method of bore sighting a gun, comprising placing bench marks on the sight yoke of the gun directly over and at equal distances above the center lines of the telescope holders, mounting a collimator support in the muzzle of the gun for rotation about the bore thereof, cross leveling the collimators by depressing the sight yoke 553. GEQMETRICAL. INSTRUMENTS.

to a predetermined range setting and rotating the collimator support until the cross lines of the collimators are in alignment with the bench marks, elevating'V the sight yoke to zero range, and adjusting the sight telescopes relatively to their supports to bring their cross lines into alignment with the cross lines of the collimators.

3. A bore sighting apparatus, comprising al collimator support mounted at the muzzle end of a gun, and collimators mounted one at each end of said support so that their axes bear a predetermined relation with respect to the axis of the bore at the muzzle.

4. A bore sighting apparatus, comprising a collimator support having two arms, and collimators mounted one n each arm of said support so that their axes bear a predetermined relation to the axis of the bore at the muzzle, the horizontal cross line of said collimator being graduated for bore sighting at various ranges.

5. A method of bore sighting a gun, comprising positioning a sighting device with its lines of sight parallel to the bore of the gun at the muzzle and in such relation thereto as corresponds respectively to the sighting telescopes, and then adjusting the sighting telescopes into alignment with the corresponding lines of sight.

6. Bore sighting apparatus, comprising a plug adapted to fit within the muzzle end of a gun, a collimator supporting arm secured to said plug, a collimator at each end of said supporting arm, means for xedly securing said plug and collimator supporting arm at the muzzle of a gun, and means for aligning said collimators relative to the bore at the muzzle of said gun.

'7. A method of bore sighting a gun, comprising establishing optical axes parallel and with a predetermined relationship to the axis of the bore of a gun at its muzzle and aligning the optical axes of the sighting telescopes of the gun with said rst optical axes.

JAMES B. NOLAN. 

